The invention relates to portable air cleaners for use in removing smoke, dust, pollen, bacteria and other particulate matter from the air through the use of filter elements such as high efficiency particulate air (HEPA) filters. A HEPA filter, by definition, has a 99.97% minimum efficiency of removing airborne particulates of a size of 0.3 microns or larger.
Portable HEPA filter air cleaners are known. For instance, U.S. Pat. No. 4,629,482 granted to G. B. Davis on Dec. 16, 1986 discloses a portable air purification apparatus which employs a cylindrical HEPA filter, which is mounted between a base and a cover, and a centrifugal fan disposed in the base to produce a purified air flow. In operation, the centrifugal fan draws unpurified air through the exposed wall of the cylindrical HEPA filter. The resulting purified air is then radially directed by the centrifugal fan through radially disposed exhaust openings in the base. Davis U.S. Pat. No. 4,629,482 further discloses that it is critical that the radially disposed exhaust openings be horizontally aligned with the centrifugal fan blades so as to produce a non-turbulent exhaust flow which is said to pulsate when the inlet flow is reduced below a certain level due to a clogged HEPA filter. This pulsation of the exhaust air flow is intended to alert the user to replace the HEPA filter.
The configuration of HEPA filter air cleaners wherein the inlet openings and the exhaust openings are both radially disposed has several significant drawbacks. First, given the proximity of the exhaust openings to the inlet openings, a portion of the exhausted purified air will be immediately recirculated back into the air cleaner. This flow pattern results in a reduced efficiency of room air purification, i.e., reduced number of complete room air changes. Second, exhaust flow through exhaust openings that are radially disposed in the lower base portion of the air cleaner may cause particulates on the flooring on which the portable air cleaner is placed, for example, carpeting, to be dispersed into the air thereby temporarily worsening the condition of the air within the room. Third, exhaust flow through radially disposed openings impinge on objects in the room, such as furniture, thereby reducing the dispersal of purified air throughout the room. The radially disposed exhaust flow also directly blows on people relatively near the air cleaner. Obviously, such direct blowing can be annoying and may lead the user to employ the air cleaner only sparingly.
Accordingly, it is an object of the present invention to provide an air cleaner having an exhaust flowpath that results in an improved efficiency of room air purification and a more thorough dispersal of purified air.
Another object of the present invention is to reduce noise levels during air cleaner operation.